1. Field of the Invention
The present invention relates to an automatic document transportation device in a scanner, a facsimile machine and a copy machine or the like, which transports an original document on a document tray through a transportation path to a scanning position and a document discharge tray.
2. Description of Related Art
A scanner, a facsimile machine and a copy machine or the like include an automatic document transportation device having an Automatic Document Feeder (ADF) which sequentially feeds a plurality of original documents. By using the automatic document transportation device, a plurality of original documents placed on a document tray can be transported continuously and automatically to a scanning position.
FIG. 8 is a cross-sectional view showing the ADF of a copy-and-facsimile Multi Function Peripheral (MFP) 900. An original document on a document tray 901 is transported by the ADF to a document discharge tray 902 provided below the document tray 901, from an upper side to a lower side in a U-turn manner. In the transportation process, an image of the original document is scanned by an image scanning unit such as a Charge Coupled Device (CCD). Specifically, as shown in the drawing, a transportation path 903 is formed from the document tray 901 to the document discharge tray 902. The original documents on the document tray 901 are transported continuously to the document discharge tray 902 by a document feed roller 904 provided in proximity to an inlet of the transportation path 903 and transportation rollers 905 provided appropriately along the transportation path 903. While the original document picked up from the document tray 901 is transported through the transportation path 903, an image scanning process is executed on one side of the original document by a CCD scanning unit 906. Downstream of the CCD scanning unit 906, an image scanning process is executed on another side of the original document by a Contact Image Sensor (CIS) scanning unit 907.
In the ADF, a document length sensor 908 and a document width sensor 909 are provided along the transportation path 903 for automatically distinguishing a document size before scanning an image of the original document. The document length sensor 908 detects a leading edge and a trailing edge of the transported original document. The document width sensor 909 includes a plurality of sensors arranged in a width direction of the transportation path 903. In accordance with each of the detection signals of the document length sensor 908 and the document width sensor 909, a control unit (not shown) distinguishes the document size before scanning the original document. Meanwhile, a sensor can be provided on the document tray 901 and the sensor can distinguish the document size. Compared with this case, the document length sensor 908 and the document width sensor 909 are advantageous in distinguishing the document size when original documents of different sizes are placed on the document tray 901.
Although not shown in the drawing, a reversal path can be formed from a downstream side to an upstream side of the CCD scanning unit 906. In a first pass of the original document, the document size can be distinguished by a pre-scanning process of the CCD scanning unit 906. Then, the original document can be returned via the reversal path. In a second pass of the original document, an image scanning process can be carried out by the CCD scanning unit 906.
As described above, in case the CIS scanning unit 907 is provided at an inner side of the transportation path 903, the automatic document transportation device is required to have a certain height so that the CIS scanning unit 907 does not interfere with other constituent members such as the transportation rollers 905. For example, in proximity to the inlet of the transportation path 903, a retard roller 910 for separating the original documents is provided facing the document feed roller 904 across the transportation path 903. The transportation rollers 905 are provided facing one another at the inner side and an outer side of the transportation path 903. Meanwhile, in proximity to an outlet of the transportation path 903, the CIS scanning unit 907 and the document discharge roller 911 are provided. In the transportation path 903 having the sideways letter-U shape, the transportation path in proximity to the inlet and the transportation path in proximity to the outlet are provided vertically in two stages. Therefore, the transportation path in proximity to the inlet and the transportation path in proximity to the outlet are required to be separated from one another for at least the height of these constituent members. However, in case a Flat Bed Scanner (FBS) is provided in the copy-and-facsimile MFP 900, the document pressing cover includes the ADF which is the automatic document transportation device. The ADF is opened and closed along with the document pressing cover. Therefore, the height of the ADF is preferable to be low.
In the conventional automatic document transportation device, for example, to distinguish whether or not a document length is a document length of a portrait direction of A4 size paper by the document length sensor 908 before scanning an image by the CCD scanning unit 906, a transportation path length from the document length sensor 908 to a read sensor 912 of the CCD scanning unit 906 is required to be the document length of the portrait direction of the A4 size paper or longer. Therefore, as shown in the drawing, the transportation path 903 is formed so that the outlet is located at an inward position compared with the inlet. Furthermore, the document tray 901 is provided at the inlet. Therefore, the original documents discharged onto the document discharge tray 902 are difficult to be confirmed visually and the original documents are difficult to be taken out. Moreover, in case the reversal path is formed and the image scanning process is carried out by passing the original document twice, if the original documents of different sizes are mixed, the pre-scanning process is required to be carried out for each of the original documents. Therefore, a period of time required for the image scanning process becomes long.